grains is easy

rust/grains/.exercism/config.json

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+{
+  "authors": [
+    "IanWhitney"
+  ],
+  "contributors": [
+    "ClashTheBunny",
+    "coriolinus",
+    "cwhakes",
+    "efx",
+    "ErikSchierboom",
+    "krodyrobi",
+    "lutostag",
+    "navossoc",
+    "nfiles",
+    "petertseng",
+    "rofrol",
+    "stringparser",
+    "TheDarkula",
+    "xakon",
+    "ZapAnton"
+  ],
+  "files": {
+    "solution": [
+      "src/lib.rs",
+      "Cargo.toml"
+    ],
+    "test": [
+      "tests/grains.rs"
+    ],
+    "example": [
+      ".meta/example.rs"
+    ]
+  },
+  "blurb": "Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.",
+  "source": "The CodeRanch Cattle Drive, Assignment 6",
+  "source_url": "https://web.archive.org/web/20240908084142/https://coderanch.com/wiki/718824/Grains"
+}

rust/grains/.gitignore

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+/target
+Cargo.lock

rust/grains/Cargo.toml

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+[package]
+name = "grains"
+version = "0.1.0"
+edition = "2024"
+
+# Not all libraries from crates.io are available in Exercism's test runner.
+# The full list of available libraries is here:
+# https://github.com/exercism/rust-test-runner/blob/main/local-registry/Cargo.toml
+[dependencies]

rust/grains/HELP.md

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+# Help
+
+## Running the tests
+
+Execute the tests with:
+
+```bash
+$ cargo test
+```
+
+All but the first test have been ignored. After you get the first test to
+pass, open the tests source file which is located in the `tests` directory
+and remove the `#[ignore]` flag from the next test and get the tests to pass
+again. Each separate test is a function with `#[test]` flag above it.
+Continue, until you pass every test.
+
+If you wish to run _only ignored_ tests without editing the tests source file, use:
+
+```bash
+$ cargo test -- --ignored
+```
+
+If you are using Rust 1.51 or later, you can run _all_ tests with
+
+```bash
+$ cargo test -- --include-ignored
+```
+
+To run a specific test, for example `some_test`, you can use:
+
+```bash
+$ cargo test some_test
+```
+
+If the specific test is ignored, use:
+
+```bash
+$ cargo test some_test -- --ignored
+```
+
+To learn more about Rust tests refer to the online [test documentation][rust-tests].
+
+[rust-tests]: https://doc.rust-lang.org/book/ch11-02-running-tests.html
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit src/lib.rs Cargo.toml` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Rust track's documentation](https://exercism.org/docs/tracks/rust)
+- The [Rust track's programming category on the forum](https://forum.exercism.org/c/programming/rust)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+## Rust Installation
+
+Refer to the [exercism help page][help-page] for Rust installation and learning
+resources.
+
+## Submitting the solution
+
+Generally you should submit all files in which you implemented your solution (`src/lib.rs` in most cases). If you are using any external crates, please consider submitting the `Cargo.toml` file. This will make the review process faster and clearer.
+
+## Feedback, Issues, Pull Requests
+
+Head to [the forum](https://forum.exercism.org/c/programming/rust/) and create a post to provide feedback about an exercise or if you want to help implement new exercises.
+Members of the rust track team are happy to help!
+
+The GitHub [track repository][github] is the home for all of the Rust exercises.
+
+If you want to know more about Exercism, take a look at the [contribution guide].
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
+
+[help-page]: https://exercism.org/tracks/rust/learning
+[github]: https://github.com/exercism/rust
+[contribution guide]: https://exercism.org/docs/community/contributors

rust/grains/README.md

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+# Grains
+
+Welcome to Grains on Exercism's Rust Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Introduction
+
+There once was a wise servant who saved the life of a prince.
+The king promised to pay whatever the servant could dream up.
+Knowing that the king loved chess, the servant told the king he would like to have grains of wheat.
+One grain on the first square of a chessboard, with the number of grains doubling on each successive square.
+
+## Instructions
+
+Calculate the number of grains of wheat on a chessboard.
+
+A chessboard has 64 squares.
+Square 1 has one grain, square 2 has two grains, square 3 has four grains, and so on, doubling each time.
+
+Write code that calculates:
+
+- the number of grains on a given square
+- the total number of grains on the chessboard
+
+## Source
+
+### Created by
+
+- @IanWhitney
+
+### Contributed to by
+
+- @ClashTheBunny
+- @coriolinus
+- @cwhakes
+- @efx
+- @ErikSchierboom
+- @krodyrobi
+- @lutostag
+- @navossoc
+- @nfiles
+- @petertseng
+- @rofrol
+- @stringparser
+- @TheDarkula
+- @xakon
+- @ZapAnton
+
+### Based on
+
+The CodeRanch Cattle Drive, Assignment 6 - https://web.archive.org/web/20240908084142/https://coderanch.com/wiki/718824/Grains

rust/grains/src/lib.rs

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+pub fn square(s: u32) -> u64 {
+    2_u64.pow(s - 1)
+}
+
+pub fn total() -> u64 {
+    (1..=64).map(|x| square(x)).sum()
+}

rust/grains/tests/grains.rs

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+use grains::*;
+
+#[test]
+fn grains_on_square_1() {
+    assert_eq!(square(1), 1);
+}
+
+#[test]
+fn grains_on_square_2() {
+    assert_eq!(square(2), 2);
+}
+
+#[test]
+fn grains_on_square_3() {
+    assert_eq!(square(3), 4);
+}
+
+#[test]
+fn grains_on_square_4() {
+    assert_eq!(square(4), 8);
+}
+
+#[test]
+fn grains_on_square_16() {
+    assert_eq!(square(16), 32_768);
+}
+
+#[test]
+fn grains_on_square_32() {
+    assert_eq!(square(32), 2_147_483_648);
+}
+
+#[test]
+fn grains_on_square_64() {
+    assert_eq!(square(64), 9_223_372_036_854_775_808);
+}
+
+#[test]
+#[should_panic]
+fn square_0_is_invalid() {
+    square(0);
+}
+
+#[test]
+#[should_panic]
+fn square_greater_than_64_is_invalid() {
+    square(65);
+}
+#[test]
+fn returns_the_total_number_of_grains_on_the_board() {
+    assert_eq!(grains::total(), 18_446_744_073_709_551_615);
+}